In recent years, expectations are growing for widespread use of various electric vehicles with a view to solving environment and energy problems. As a key to wide spread use of these electric vehicles, vigorous development of secondary batteries as an in-vehicle power source such as a power source for driving a motor is under way. However, in order for the electric vehicles to gain wide acceptance, the batteries need to have higher performance and be less expensive. Further, there is a need for the single-charge travel distance of the electric vehicles to approach that of gasoline engine vehicles, giving rise to the demand for batteries having higher energy density. In order to allow a battery to have a high energy density, there is a need to reduce a battery member, which is not directly involved in a battery reaction, as much as possible. A bipolar type secondary battery has been proposed as a battery in which a current collecting tab of a battery single cell, a bus bar for connection between single cells, and the like can be saved and which is very excellent in volume efficiency and suitable for vehicle installation. The bipolar type secondary battery uses a bipolar type electrode in which a positive electrode is formed on one surface of one current collector and a negative electrode is formed on the other surface thereof. Further, the bipolar type secondary battery has a structure in which a plurality of the bipolar type electrodes are laminated via a separator including an electrolyte layer such that the positive electrode and the negative electrode face each other. Therefore, in this bipolar type secondary battery, one battery cell (single battery) is formed by the positive electrode, the negative electrode, and the separator (the electrolyte layer) which are provided between the current collector and the current collector.
For example, in order to improve an output density per weight of the secondary battery, Patent Literature 1 has proposed to use a current collector containing a polymer material and a conductive filler.